On December 4, 2025, the USGS-operated ShakeAlert earthquake early warning system generated a false alert for a non-existent magnitude-5.9 earthquake near Carson City, Nevada. This error resulted in alert deliveries by ShakeAlert Partners through the Federal Emergency Management Agency's (FEMA) Wireless Emergency Alert (WEA) system, the MyShake app, and cell phone operating systems. Based on the preliminary technical analysis conducted to date, a combination of issues contributed to the false alert:

• The ShakeAlert System received data from five seismometers near the California-Nevada border that were incorrectly interpreted by the ShakeAlert Processing Center as a M5.9 event.
• Three of the stations produced false readings due to malfunctioning communications between Reno and the ShakeAlert Data Processing Centers.
• A fourth station produced a false reading due to a seismometer malfunction, and a fifth station, located in an urban environment, triggered on local noise, a common occurrence for stations surrounded by high anthropogenic activity, although such triggers are rarely large enough in amplitude to be of concern.

The ShakeAlert internal processing software systems have safeguards in place to try to prevent the delivery of false alerts from these kinds of signals, but these controls proved insufficient in this case. As these issues continue to be investigated, the lessons learned will be used to improve the system safeguards, including changes to how software recognizes and processes false triggers. We are working to integrate changes to prevent future false alerts while maintaining the requirement for extremely rapid earthquake detection and alert delivery.